Edlebrock 1405 Carb

I've looked in the tech archive and didn't see any postings re this carb. I'm having a ***** of a time getting out the last of the surging and flat spot with my Edlebrock 1405 carb (600 cfm). It's on a SBC 350 which has a Comp 280 cam, flat top pistons, and an air gap manifold. In the cruise mode with just a tiny bit of throttle it surges. When the throttle is first opened (barely) there is a flat spot. I bought the Edlebrock kit with all the metering rods, jets, and springs. I've gone through three of their suggested changes for surging and flat spots. It has improved but I think it should be better. I also adjusted the acclerator pump to its max stroke. It goes like hell when you mash it but it's the slow cruising speed where the irritating surging takes place. Has anyone else mastered this problem?

Thanks

 

Wow, I have a 1406, and I have been having some problems similar to that that I chalked up to a bad motor (pulled a rebuild that was screwed up and threw in a junk one from the shop floor). Both motors seemed to do this.... Could it be the carb?

 

Mike,

Could be the carb. This engine is all new rebuilt so there shouldn't be any problem with it. I have a 1406 on a stock Chev 283 in my panel truck. I took it out of the box, slapped it on, and drove it. No adjustments needed. It has not been any problem except it has a little hesitation when you round a sharp corner. Otherwise it runs great. The 1405 has been a pain. I guess I will have to find a good carb man to help me out.

 

Isn't a 1406 just a 1405 with an electric choke?

 

No, there is a tiny difference in the jets and metering rods.

Curious note. I priced an electric choke for my 1405, $70+, I choked myself. I put on a cable.

 

Have you tried a change to a lighter metering rod spring?

Vacuum holds em closed and the springs raise em up.
Sounds like the low vacuum levels caused by the big cam are allowing the springs to pop the rods up before they should.
The rods may be coming up at idle giving you an overly rich idle mix as well.

If the springs do the trick, go back to the mid-point hole on the accelerator pump.

 

Thanks for the suggestion C9. I'll try it.

 

C9,

Well, I've tried every spring in the box, weaker and stronger. The problem is still there. I think I'm going to have to "seek professional help" to sort out the problem. In checking the vacuum, I have 12 in. at an idle of about 850. I have a maximum of 24 in. at higher throttle settings. The strongest spring is rated for 8 in. manifold vacuum.

Thanks again,

 

Hey 3by-
Have you tried putting in the rods with the smallest "cruise" diameter size in your kit? The tips of the rods are for "power" mixture when the throttle is open and vac is low,and the section of the rods above the tips are for "cruise" mixture.Sounds lean to me,and a richer cruise mix may fix it.If it almost fixes it but still needs a bit,go up one jet size in the primaries too.
chicken

 

Thanks Chicken. I will check to see if that was one of the rods I have tried.

 

Poor combination of parts..............in my humble opinion........too small a carb and too much a high RPM intake......it runs OUT of CFM when the intake gets to it's RPM range......


Also..........not being a smart a$$ but sometimes ...........the threaded hole in the rear of the Edelbrocks makes a vacuum leak......had a fellow I know chase his hiney for a week......trying to fix some of the same issues you are having.......had low vacuum ......

Took the Edelbrock off.........installed a new THICK gasket and put a little sealer in the rear hole threads ( vacuum for the trans/brake ...whatever ) and reinstalled the br*** pipe plug............it got a whole lot better.......

.

 

Deuce,

I will check for vacuum leaks, particularly the plug you mention. I don't think my problem, which is at low and just opening throttle speed, is related to insufficient CFM's. It goes like hell when I mash it, but I've only had it up to about 80 so far.

You may be right about the carb needing to be bigger for all out power though. The engine builder suggested the 600 CFM, a guy at the parts store said, "Nahhh, you need a 750". So, I'm trying the 600 and will change if needed. Meanwhile I just want it to quit bucking and surging at minimum throttle.

Thanks,

 

Well I may be wrong........... about your intake......

I just got a new Edelbrock catalog.......one day last week. Looked at it this morning and Edelbrock has a Performer Air Gap.........RPM range idle to 5500RPM. IF that's the one you have......or the RPM Air Gap....( 1500 - 6500 RPM ) your intake is good for your combination........

I thought you had the first ( and only ones I knew about..til this morning ) Edelbrocks with air gaps between the runners and the bottom of the intake. Those air gaps type RPM range is 3500 to 8000 RPMs.

I ran a Victor Junior on a engine that I fixed for a dirt track buddy.....It really came on after 4500 RPMS............but was a dog at lower RPMS.....

 

I have sold and used the Edelbrock carbs for almost 20 years.The single biggest issue with these carbs is fuel pressure.Too much (more that 5-1/2 lbs) will cause surging and stumbling.Call any Edelbrock tech,and this is the first thing they recommend to do,install a gauge.I had similar problems years ago.Changed jets,step-up springs,metering rods,basically no change.I stuck a gauge on there,and was surprised to find that a $9.00 stocker fuel pump was able to put out 10lbs of pressure.Installed a Holley #12-803 regulator,adjusted to 5-1/2lbs,problem solved.

Try that,it may be your problem.